Two stage pulping process including impregnating chips with ammonia, then liberating the ammonia and pulping with magnesium compound



United States Patent TWO STAGE PULPING PROCESS INCLUDING IM- PREGNATING CHIPS WITH AMMONIA, THEN LIBERATING THE AMMONIA AND PULPIN G WITH MAGNESIUM COMPOUND Theodore E. Kloss, Waterville, Maine, assignor to Allied Chemical Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Dec. 12, 1963, Ser. No. 329,944

6 Claims. (Cl. 16215) ABSTRACT OF THE DISCLOSURE A process for preparing pulp which includes a digesting of cellulose materials in an aqueous solution of an ammonium compound, adding a magnesium compound to the solution before the formation of ammonium lignosulfonates, recovering ammonia from the solution, and continuing the digestion of the cellulose materials with the magnesium compound solution.

This invention relates to the digestion of wood chips or other ligno-cellulose materials to produce the pulp with free fibers thereof, more particularly to a two-stage fiber liberating process utilizing ammonia in the first stage.

Ammonia and ammonium compounds of various forms are known as effective for use in cooking liquors for the digestion of wood chips and like cellulose materials to separate the ligneous and other components of the wood from the cellulosic fiber. In spite of its efliciency in the process, ammonia has not gained any appreciable popularity in application, in view of the fact that its use can become economical only if substantial amounts of ammonia can be recovered. In the prior art various methods for the recovery of ammonia have been suggested, but all of these processes are aimed at recovering the ammonia from the spent cooking liquor by flashing it off with magnesium compounds, pyrolysis, or the like methods. The ammonia in the spent liquor is present in a combined form as the ammonium salts of lignin sulfonic acid and sugars, making the recovery of reusable ammonia difiicult and often inefiicient.

It is an object of the invention to provide a process whereby ammonia is recovered from the digester in a form whereby it can be reused for the defibering process.

In accordance with the invention it has been discovered that the ammonia-containing cooking solution is the most effective as a penetrating agent for the wood chips and the like cellulosic materials at the initial part of the cooking process. Accordingly, the present invention contemplates subjecting the cellulosic material to the penetrating action of an ammonium compound and subsequently liberating ammonia with a magnesium compound before the formation of ammonium ligno-sulfonates occurs, and continuing the digestion of the cellulosic material with the magnesium compound used in the liberation of the ammonia. By the use of the process of the invention, the ammonia can be efiiciently and economically recovered, and in a form capable of reuse for subsequent digestions.

As used in the specification and the claims, the term digester is intended to designate any vessel or chamber, wherein wood chips or other cellulosic materials are freed from their content of non-cellulosic matter, before the cellulose is discharged into a blow pit; and the term cellulosic material is intended to include wood chips and other ligno-cellulose materials, from which the fibermaking pulp is produced.

For the initial phase of the digestion process of the invention a digesting liquor is prepared by combining ammonia, water, and sulfur dioxide to form, depending on the conditions, an ammonium sulfite or ammonium bisulfite solution, in a known manner. Generally a 1.5

to 6 percent by weight, based on NH aqueous solution is used. The wood chips and the digestion liquor are heated together, in most cases at a temperature between C. and 180 C. for 2-8 hours total digestion time, depending on the type of cellulosic raw material and pulp requirements. In accordance with the invention, the first pulping phase with the ammonia-containing liquor is completed within 15-35% of the total cooking time including the time required to heat the liquor to the cooking temperature. At this initial stage, the ammonium compound has not combined to any large extent with the lignin content of the cellulosic material, but accomplishes a vigorous and substantial penetration thereof. Subsequently a substantially equimolar quantity of a magnesium compound, such as magnesium hydrate as a slurry is then added to the digester and the cooking process is continued. The ammonia content of the first digesting solution is thereby recovered in a gaseous form at the top of the digester, where it can be recirculated to prepare the makeup liquor for a subsequent digestion cycle.

The fiber-liberation process is subsequently completed in the magnesium-base cooking liquor, and the free fibrous material is recovered in the blow pit in the usual manner. The magnesium-base spent liquor can be processed to recover magnesium oxide by any usual recovery technique, such as pyrolysis.

Since the sulfite ion concentration is the means by which a suitable control of the pulping process can be maintained, it is contemplated that additional S0 could be introduced into the first or second cooking liquors at any time during the process, most conveniently at the time the ammonia is flashed off by the subsequent addition of the solution containing the magnesium compound.

The process of the invention can be readily combined with some prior art cooking solutions utilizing alkali or earth alkali sulfites, by using a mixture of the ammonium sulfite with the alkali or earth alkali sulfites in the initial cooking stage. The ammonia can be flashed off by the magnesium compound also in the presence of the alkali and earth alkali sulfites.

In the following, an example is disclosed which utilizes the process of the invention.

Example- A digesting liquor is prepared by combining ammonia, water and sulfur dioxide, the liquor containing 1.06 percent by weight ammonia and 4.0 percent by weight S0 sufficient to provide a formula ratio NH HSO Wood chips (#1 part by Weight) are heated in a digester together with the ammonia-containing solution (5 parts by weight) at C. under autogenous pressure for one hour. Subsequently an equimolar quantity of magnesium hydrate is added in a slurry to the first cooking liquor thereby liberating ammonia at the top of the digester, from where it is recovered for reuse by absorption in an SO -containing solution. The cooking in the magnesium-containing liquor is continued for another 5 hours, and the cellulosic pulp is recovered in a blow pit in conventional manner.

It is to be understood that while a two-stage process is contemplated wherein the ammonia-containing cooking liquor is replaced by a magnesium compound-containing solution, small amounts of ammonia in the second cooking liquor or, conversely, small amounts of the magnesium compound in the ammonia-containing cooking liquor will not materially affect the efficiency of the process. Therefore, the full scope of the invention is to be interpreted from the appended claims.

I claim:

1. A plural-stage pulping process which comprises penetrating a cellulosic material with an aqueous solution of a fiber-liberating ammonium compound, adding a magnesium hydrate to said solution prior to any substantial formation of ammonium ligno-sulfonates, recovering ammonia from the solution, and continuing the pulping process with said magnesium hydrate-containing solution.

2. The plural-stage pulping process of claim 1, wherein said ammonium compound is selected from the group consisting of ammonium sulfite and ammonium acid sulfite.

3. The two-stage pulping process of claim 2, wherein the solution of said magnesium hydrate contains sulfite.

4. A method for preparing sulfite pulp comprising the steps of digesting cellulosic material to be defibered with a solution of an ammonium sulfite compound, subsequently adding a magnesium hydrate to said solution to liberate ammonia before any substantial combination thereof with the non-cellulosic components of said cellulosic material, recovering the liberated ammonia and concluding the digesting in said solution of the magnesium hydrate.

5. A two-stage defibering process for cellulosic material, which comprises subjetcing the cellulosic material to the action of a solution of an ammonium compound, adding a magnesium hydrate to replace the ammonium compound so as to complete the defibering therewith, recovering the replaced ammonium hydrate prior to the completion of the defibering process.

6. The process of claim 4, wherein the digestion period in the ammonia-containing solution is less than 50% of the entire digestion period.

References Cited UNITED STATES PATENTS 1,891,337 12/1932 Seaman 16286 X 1,910,613 5/1933 Kylander 162-63 X 2,041,745 5/ 1936 Dreyfus 16286 DONALL H. SYLVESTER, Primary Examiner.

HOWARD R. CAINE, Examiner. 

1. A PLURAL-STAGE PULPING PROCESS WHICH COMPRISES PENETRATING A CELLULOSIC MATERIAL WITH AN AQUEOUS SOLUTION OF A FIBER-LIBERATING AMMONIUM COMPOUND, ADDING A MAGNESIUM HYDRATE TO SAID SOLUTION PRIOR TO ANY SUBSTANTIAL FORMATION OF AMMONIUM LIGNO-SULFONATES, RECOVERING AMMONIA FROM THE SOLUTION, AND CONTINUING THE PULPING PROCESS WITH MAGNESIUM HYDRATE-CONTAINING SOLUTION. 